Liquefied petroleum gas (LPG) such as propane is frequently stored for use in relatively small tanks. This is particularly true for consumer applications. LPG products have a substantial coefficient of expansion, and with a change in temperature, the volume of liquefied gas can contract or expand substantially. Since liquids are noncompressible, any expansion of the fluid in the tank can possibly cause a hazardous overpressurized condition. To prevent the occurrence of such a condition, tanks must be filled only to a specified maximum liquid level at ambient conditions to leave sufficient vapor space to accommodate the greatest possible expansion of the the liquid. Automatic stop-fill valves have been developed to control the amount of liquid stored in the LPG tank. Such a valve is shown in U.S. Pat. No. 4,313,459. However, such stop-fill valves can shut off the flow of fluid when different quantities have been received into the tank depending on the temperature of the fluid. To ensure safe operation, such valves must be set to shut off at a relatively low volume level, and as a result the tank is not necessarily filled to the optimum level.
It is desirable to fill an LPG tank with the maximum amount of fluid for convenience of use while maintaining a safe pressure level in the tank. In view of these requirements there exists a need for a float mechanism for use with a stop-fill valve for gauging the quantity of the LPG in the tank independent of the density, and therefore temperature, of the fluid.